A garage base carries real loads — a car is 1.5–2 tonnes concentrated on four small contact patches, plus the weight of the structure itself. This is the spec we supply concrete against for garage and workshop bases across West Yorkshire.
The build-up, bottom to top
- Sub-base: 150mm compacted MOT Type 1, level and true
- Sand blinding: 25mm to protect the membrane
- DPM: 1200-gauge polythene, joints lapped 300mm and taped
- Concrete: 150mm of C30 with A142 mesh on 50mm spacers
- Edge thickening: 300–400mm deep × 300mm wide under wall lines for sectional or brick garages
Volumes and cost
At 2026 prices (all concrete £125/m³ — premium C35 mix as standard):
- Single garage (3 × 6m): ~3m³ with edge thickening ≈ £375
- Double garage (6 × 6m): ~6m³ ≈ £750
- Workshop slab (8 × 6m): ~8m³ ≈ £1,000
Because volumetric trucks mix on-site, you can pour the thickened edge and the main slab from the same visit and pay only for the metreage used — check yours on the calculator.
Pour-day tips
- Pour the perimeter thickening first, then flood the main slab while it is still wet so everything bonds monolithically
- Tamp level, then power-float or steel-trowel once the surface has stiffened for a dust-free finish
- Cut or trowel a control joint if either dimension exceeds 6m
- Keep vehicles off for 7 days minimum — full strength takes 28 days (curing explained)
Building Regulations note
Detached garages under 30m² are usually exempt from Building Regs, but the slab still needs to be right — a failed base means a twisted door frame within a year. If in doubt about ground conditions (clay, old drains, made-up ground), dig test holes and thicken accordingly, or talk to us — we pour foundations daily and are happy to advise.
Book your pour on the booking page or call 01924 910 129.
FAQs
How thick should a concrete garage base be?+
150mm of concrete is the standard for a domestic garage, laid over 150mm of compacted MOT Type 1. Include A142 steel mesh in the middle of the slab and thicken the edges to 300–400mm where the walls will sit.
What grade of concrete for a garage base?+
C30 minimum. It handles the point loads of a car, resists oil and gives a hard-wearing surface. For workshops with lifts or heavy machinery, use C35.
Do I need a damp-proof membrane under a garage base?+
Yes — a 1200-gauge polythene DPM under the slab (lapped up the edges) stops rising damp, keeps the slab dry and is required if the garage will ever be converted or heated.
How much concrete does a single garage base need?+
A typical 3m × 6m single garage at 150mm needs 2.7m³. A 6m × 6m double needs about 5.4m³. Thickened edges add roughly 10–15%.